Superjunction structures are well known in the art and are described, for example, by Fujihira, “Theory of Semiconductor Superjunction Devices,” Jpn J. Appl. Phys., Vol. 36 (1997), pp. 6254-6262; Fujihira and Miyasaka, “Simulated Superior Performance of Semiconductor Superjunction Devices,” Proc. of 1998 Symposium on Power Semiconductor Devices & ICs, Kyoto, Japan, pp. 423-426; Strollo and Napoli, “Optimal ON-Resistance Versus Breakdown Voltage Tradeoff in Superjunction Power Devices. A Novel Analytical Model,” IEEE Transactions on Electron Devices, Vo. 48, No. 9, September 2001, pp. 2161-2167; and Gerald Deboy, “The Superjunction Principle as Enabling Technology for Advanced Power Solutions”, IEEE ISIE 2005, Jun. 20-23, 2005, Dubrovnik, Croatia, pages 469-472. In its simplest form, superjunction structures employ a number of alternatively arranged P and N doped semiconductor layers or regions, with the condition that the doping of these layers are charge-balanced, or Na*Wa=Nd*Wd, in which Na and Nd are the doping concentrations of the P and N layers, and Wa, Wd, the widths of these same layers. Current flow through such superjunction structures is for the most part parallel to the planes of the P-N junctions. Superjunction structures are often employed in high voltage (and high power) semiconductor (SC) devices in order to obtain comparatively high breakdown voltages while minimizing series ON-resistance. The superjunction structures facilitate this desirable combination of properties. Superjunction devices are also available on the open market, as for example, the CoolMOS™ family of devices produced by Infineon of Villach, Austria.
It is known to utilize superjunction structures in trench-type power devices. FIG. 1 illustrates prior art N-channel trench-type metal-oxide-semiconductor (Trench-MOS) device 20 employing superjunction structure 21 in drift space 22 between trench-type channels 23 and drain 29. Device 20 comprises N+ substrate (e.g., drain) 29 on which has been formed superjunction structure 21 comprising multiple parallel vertically arranged N-type regions 25 and P-type regions 26, of for example silicon, with intervening PN junctions 27. Lower portion 28 of superjunction structure 21 contacts substrate 29, which together with electrical contact 291 forms the drain of Trench-MOS device 20. P-type body region 32 is located above drift space 22 comprising superjunction structure 21. Trench 31 extends from upper surface 39 through body region 32 to upper portion 35 of superjunction structure 21. Trench 31 is lined with gate dielectric (e.g., SiO2) 36. The interior portion of trench 31 within gate dielectric 36 is filled with gate (e.g., doped poly-silicon) 38 having gate contact 381. N+ source regions 34 with source contacts 341 are formed in P-type body region 32 on either side of trench 31, insulated from gate 38 by gate dielectric 36. When appropriately biased, source-drain current 30 (abbreviated as “ID”) flows from source contact 341 and sources 34 through substantially vertical channels 23 in P-type body region 32 into drift space 22 formed by N-type regions 25 of superjunction structure 21 to drain region 29 and drain contact 291. Long dimension 37 of trench 31, gate 38 and sources 34 is substantially perpendicular to the planes of parallel N and P regions 25, 26 and intervening PN-junctions 27 of superjunction structure 21.
While the structure illustrated in FIG. 1 is useful, it is desirable to improve its properties. Accordingly, there is a need for improved device structures and methods of fabrication that can provide improved performance. It is desirable to provide trench and superjunction type semiconductor devices that offer, for example, improved carrier mobility while still being able to be fabricated using conventional processing equipment and process chemistry. Further it is desirable to provide an improved device structure and method of fabrication that is useful with a variety of semiconductor materials. Furthermore, other desirable features and characteristics of the various embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.